Method of and apparatus for interconnecting lined pipes

ABSTRACT

There are disclosed methods of and apparatus for interconnecting lined metal pipes ( 110, 120 ), applying in particular to the offshore oil and gas industry. Corrosion is a common problem in the industry. Lining pipes overcomes the problem, but welding sections of pipe together can be a complicated and time-consuming task, requiring dedicated and sophisticated tooling. More desirable is the ability to use conventional pipe-laying equipment ( 20, 40, 50, 60, 70, 80, 90 ) with little additional tooling. As such, there are disclosed methods and apparatus compatible with known offshore connection methods, particularly where the spacing of joints on the pipe is less than 100 m. The chosen technique will not significantly impact the laying rate of the lined pipe, compared with unlined pipe. The method includes connecting lined pipes ( 110, 120 ) using a corrosion-resistant bridging member ( 102 ) internally overlapping both linings, leaving a void space ( 146 ) behind the weld region ( 109 ) while at least the initial stages of welding ( 180 ) are performed, and expanding ( 170 ) the bridging member to provide a seal against the liners, in a controlled sequence. There is also disclosed a bridging member ( 102 ), tooling ( 170 ) and pipelay apparatus suitable for use with this method.

This invention relates to methods and apparatus for interconnectingmetal pipes lined with plastic or other deformable corrosion-resistantlining material. The invention finds particular application in theoffshore oil and gas industry, but is not limited to such applications.

Steel pipes are commonly used for the transport of fluids of differenttypes in the offshore industry. When conveying oil and gas, corrosion isa limited problem. Offshore field operators also need to transport morecorrosive fluids, in particular seawater for pumping water into a waterinjection well head. The invention is not limited to application forwater injection, or to offshore applications. Experience shows thatwater injection pipe suffers from rapid degradation due to corrosion ofthe steel pipe. In order to provide a suitable service life when usingunprotected steel pipe, the wall thickness would have to besignificantly increased, making it heavier, more expensive and moredifficult to install, especially in deep water. A very expensivesolution would be to use corrosion-resistant metal, such as Inconel™ orstainless steel. Alternatively, steel pipe with internal thermoplasticliner can be used, satisfying both weight and cost budgets.

When using lined pipe for offshore applications, the lined pipe istypically fabricated on shore using the Swagelining™ technique, asdescribed for example in United Kingdom patent GB 2186340. A slightlyoversized liner pipe made of thermal plastic material is pulled throughthe pipe using a reducing die. Once the pulling operation is completedand the pulling tension released, the liner over a period of timeprogressively returns to its original shape, locking itself inside thesteel pipe. Single lengths of pipe over 1000 m in length can bepre-fabricated and lined by this technique. If longer pipes arerequired, sections of lined pipe are then interconnected using theWeldlink™ welding process, as described in GB 2298256. This processconsists of swaging a corrosion-resistant sleeve to terminate each pipesection and then welding both the sleeves and pipe materials usingdedicated welding procedures and welding equipment. Multiple weldingoperations are required for each pipe section being joined. The timetaken for these operations is best measured in hours, but this is notprohibitive when joints are being made only once every kilometre ormore.

Using these known techniques to produce offshore pipe requires settingup a dedicated fabrication, assembling and reeling base. A reel layingspread is also required to transport and lay the pipe offshore. In somecircumstances this technique is not commercially attractive due to thecosts associated with setting up the base and the limitation of the reellay vessel (storage capacity, laying tension). As an alternative thepipe could also be bottom-towed to the offshore field after beingassembled and fabricated. However this technique also has severelimitations, such as crossing of existing pipe and complications causedby the nature and profile of seabed.

To construct a continuous pipeline it would, ideally, be possible to useexisting offshore pipe laying techniques, such as S-Lay or J-Lay, whichfabricate a continuous pipeline from a large number of shorter steelpipe sections, on board a pipe laying vessel. The pipe sections thenwould be pre-lined with lengths of thermoplastic liner. U.S. Pat. No.5,975,802 (Willis) and U.S. Pat. No. 6,213,686 (Baugh) describe twodifferent pipelaying systems of this kind. In US '802, a series ofwelding and test stations, spaced along the deck of a pipe layingvessel, operate in parallel to build the pipe rapidly from singlesections. The welded pipe is then bent upwardly and then downwardly tobe launched into the sea at the desired angle. In more conventionalJ-Lay processes, such as that described in US'686, double or quadruplepipe sections are pre-fabricated, and then up-ended in a special towerstructure, to be welded onto the end of the pipe as it is paid out. Suchsystems are highly developed and each section can be aligned, welded,tested and paid out in a matter of minutes.

As noted above, due to the complexity of the pipe fabrication andwelding procedure, the time for interconnecting each new section oflined pipe by the known Weldlink™ technique can be measured in hours,lather than minutes. As a consequence, the method is not commerciallycompatible with the known techniques for laying steel offshore pipe,which involve welding in relatively rapid succession much shorter pipesections at the field, thus forming a continuous pipe.

Another proposal for joining lined pipes is described in U.S. Pat. No.6,226,855 (Lattice), which uses a specially-formed corrosion-resistanttubular bridging member, swaged internally to seal to the liner oneither side of the joint. The steel pipe sections are then weldeddirectly to one another. This is simpler than the Weldlink™ technique,requiring only a single weld per joint, but is not available as acommercial process, and a number of issues remain to be resolved. Inparticular, the bridging member of US '855 has an intermediate sectionwhich is of increased outer diameter and of thicker material. Thisintermediate section apparently acts as a backing ring to the weld.Backing rings will in general be imperfectly welded to the pipe metal,and therefore the metal behind the weld is prone to corrosion,particularly because the ring is of different material to the pipesbeing welded. Some engineers also believe backing rings cause stressconcentration. Experiments would also be required to determine howparameters of the highly-developed and automated welding processes wouldhave to be adjusted to take account of the presence of the backing ringas a beat sink. There is also the problem that the bridging member willconduct welding heat into the plastic liner, damaging it. US '855proposes a second embodiment having a heat-barrier ring behind the weld,but this only increases the complexity of the construction. Finally, thejunction between the sealing portions and the thicker intermediateportion may be a source of weakness, under the forces applied during theswaging process.

Considering the foregoing matters, it is an object of the invention toprovide a method of and apparatus for interconnecting lined pipes thatis compatible with known offshore connection methods, particularly wherethe spacing of joints on the pipe is less than 100 m. Ideally, thechosen technique will not involve any reduction in the laying rate ofthe lined pipe, compared with unlined pipe.

In accordance with a first aspect of the present invention, there isprovided a method of joining plastic-lined conduits comprising thefollowing steps, not necessarily in the following order:

-   -   providing a first conduit and a second conduit, each conduit        comprising a wall of metal defining a bore having an open end        for connection and being substantially lined by a plastic liner,        the liner ending within the bore to leave a short unlined        section at the open end of the conduit;    -   arranging said first and second conduits with their ends        abutting;    -   welding said ends together to form a longer conduit;    -   providing a tubular bridging member of corrosion-resistant        material dimensioned to fit inside the lined conduits, the        bridging member having a first sealing portion toward one end        thereof and a second sealing portion toward the second end, said        sealing portions being interconnected by an intermediate        portion, the length of said intermediate portion being        sufficient to bridge the unlined portions of the abutting first        and second conduits while the first and second sealing portions        overlap said liners within the first and second conduits        respectively;    -   with the first sealing portion of the bridging member located        within the first conduit and overlapping the liner, expanding        said first sealing portion radially so as to press the first        sealing portion against the liner to form a first seal between        the liner and the bridging member; and    -   with the second sealing portion of the bridging member located        within the second conduit and overlapping the liner of the        second conduit, expanding said second sealing portion radially        so as to press the second sealing portion against the liner to        form a second seal between the liner and the bridging member,    -   whereby the liners, the first and second seals and the bridging        member form a continuous barrier between the interior bore of        the lined conduits and the metal of the conduit walls, wherein        the dimensions of the bridging member and the sequence of the        method steps are such that the material of the bridging member        is not located against the inside of the abutting ends of the        conduits during at least an initial pass of said welding step.

In a preferred embodiment, the ends of the lined conduits are broughttogether before the bridging member is introduced to said conduits atthe location of the abutting ends.

In this case, the bridging member may be installed via the secondconduit and subsequently expanded, after the conduits have been weldedtogether.

The bridging member may be present behind the abutting ends of theconduits prior to starting said welding step, or may be introduced afterat least an initial pass of welding has been completed. (Welding isconventionally performed by a “root pass” and several further passes forfilling and capping the weld.)

In the case where the bridging member is present at the start ofwelding, the outer diameter of the bridging portion is sufficient toleave a substantial gap behind the abutting ends.

In the alternative case where the bridging member is introduced behindthe weld location after the welding has started, the outer diameter ofthe bridging member is sufficient to allow free passage of the bridgingmember longitudinally through the lined portions of the conduits.

In alternative embodiments, the bridging member is fitted to the firstlined conduit and the first sealing portion is expanded to form saidfirst seal, with said second sealing portion and part of theintermediate portion remaining outside the first conduit, before theends of the first and second conduits are brought together. Followingthese steps it is possible to fabricate pipe sections with bridgingmember pre-fitted, to reduce the number of steps performed at sea.

The method may further comprise, at a time after said first pass ofwelding and after introducing the bridging member at the location of theabutting ends, expanding the intermediate portion of the bridging memberradially so as to substantially eliminate said space. Doing so minimisesthe quantity of corrosive fluid, such as air or sea water, retainedwithin the region, thus maximising the life of the weld. The expandingof said intermediate portion may be performed prior to expanding thefirst and second sealing portions, to allow escape of the trapped fluid.

The expanding of any of said intermediate portion and first and secondsealing portions may be performed concurrently with subsequent passes ofwelding.

Expansion of said first and second sealing portions may be provided by asingle tool comprising first and second means for radial expansion ofsaid sealing portions.

Said tool may further comprise means for radial expansion of saidintermediate portion. The expanding of said intermediate portion may beperformed by fluid injection into the region between said first andsecond radial expansion means. The first and second expanding means maybe operated with a restricted force to serve as sealing means duringsaid fluid injection.

The bridging member and expansion means may be introduced together intothe conduit and located adjacent said abutting ends. The expansion meansmay be operated with restricted force to engage the bridging membermechanically to carry it to the desired location.

This allows a combined step of locating the bridging sleeve and swagingtool between two sections of newly-welded pipe, bridging internallybetween both liners, and expansion of the sealing portions to effect acomplete seal.

The bridging member may be fabricated out of corrosion-resistant metal,for example Inconel™, or from a non-metallic material.

At least one formation may be provided on each sealing portion toimprove grip between the bridging member and the liner. In a preferredembodiment, each sealing portion is provided with a series ofcircumferential formations. Alternatively, adhesive may be used.

The end of the bridging member may be chamfered to aid insertion of thebridging member into the lined conduit.

At each end to be joined the liner end face may be chamfered to reduceits cross-sectional area. This can aid the process of introducing thebridging member into the liner, and also reduces stress in the materialof the bridging member in embodiments where the intermediate portion isexpanded over the end of the liner.

The first and second conduits may be joined as part of an offshore pipefabrication and laying process, each conduit being a section of pipelineadded in turn to the pipeline being laid by repeating the steps of themethod as set forth above. The sections may be less than 100 m long,requiring a relatively large number of joining operations, butovercoming the disadvantages associated with handling lengthy pipesections, hundreds or even thousands of metres long.

The first conduit may be either the pipe section joined already to thepipeline, or may be the one being added. In the first case, the secondconduit becomes the first conduit after the second conduit has beeninterconnected with the first conduit. In the second case, the secondconduit becomes the first conduit after interconnection.

The joining method may be performed while the first and second conduitsare substantially horizontal, the assembled pipeline being bent firstupwardly and then downwardly for entry into the sea.

Alternatively, the joining method may be performed while the first andsecond conduits are inclined at an angle for entry into the sea. In aJ-Lay vessel, where the pipe sections are paid out using a travellingclamp in an inclined tower, the expanding may be performed by a swagingdevice mounted in the head of the tower.

In accordance with the preferred embodiment mentioned above, thebridging member may be introduced at the location of the abutting endsafter the first and second conduits have been brought together.

The bridging member may be carried to the location of the abutting endsby means of an expanding tool, which engages the inside of the bridgingmember by friction. The expanding tool may comprise expanding meansoperated so as to engage the bridging member with restricted force tocarry it to the location of the abutting ends, and then with greaterforce to perform the expanding step of the sealing portions.

In such an embodiment, the expanding tool is preferably provided withfirst and second expanding means, spaced to coincide with the first andsecond sealing portions, the carrying step and expanding of the firstand second sealing portions being performed without disengaging the toolfrom the bridging member.

Alternatively, a single expanding means may be moved longitudinally toexpand different portions of the bridging member sequentially.

In alternative embodiments, the bridging member may be introduced to thefirst conduit, and the first sealing portion expanded prior to elevationof the first conduit to said angle. This saves time at the weldingstation, and may also prevent the bridging member falling into or out ofthe pipe during elevation. Alternatively, the bridging member may beheld in position initially by some sort of gripping device until it isheld in place after expanding.

Bridging members may be introduced to a plurality of lined conduitsections, prior to joining any two of the conduits together. Theassociated sealing portion may also be swaged at the same time. This canbe performed for all pipe sections at a yard onshore if desired, andwill save time at the welding station. Protective caps or collars can beapplied, to prevent damage to the projecting parts of the bridgingmember, for storage and transit.

The invention in a further aspect provides a tubular bridging memberadapted for use in the connecting method according to the invention asset forth above.

The invention yet further provides an expansion tool adapted for use inthe connecting method according to the invention as set forth above.

In accordance with a further aspect of the present invention, there isprovided an expansion tool operable for expanding at least one portionof a bridging member for joining plastic-lined conduits, said toolcomprising at least two means for radial expansion held at alongitudinal separation along the axis of the conduits, dimensioned tofit into said bridging member prior to expansion, each said expansionmeans operable with at least one selectable expansion pressure, saidtool further comprising a means for conveying the tool to its desiredlocation, in use. Said conveying means may be a main tether from whichthe tool is suspended under the influence of gravity, or an elongatemember for locating the tool within the conduits, where gravity cannotbe used to pass the tool through said conduits.

The expansion tool may further comprise a means for radial expansion ofa portion of said bridging member located between said expansion meansand may comprise fluid injection into the region between said expansionmeans. Said fluid may be transported to said tool via a pipe of smallerdiameter than the lined conduits, or via a pipe within the main tether.

Each said expansion means may be operated singly, or concurrently withat least one other expansion means, in any combination.

The invention yet further provides a pipe laying apparatus adapted forjoining lined pipes by a method according to the invention as set forthabove.

The invention yet further provides a pipe laying apparatus including anexpanding tool according to the invention as set forth above.

The invention yet further provides in combination a plurality of linedmetal pipe sections and a corresponding plurality of bridging memberssuitable for use in assembling a pipeline by a method according to theinvention as set forth above.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, by reference to the accompanying drawings, in which:

FIG. 1 shows a pipe laying vessel suitable for adapting to the existingpipe joining methods of the present invention;

FIG. 2 is a cut-away diagram of a tubular bridging sleeve of a firstembodiment of the present invention, used to bridge internally betweentwo sections of lined pipe being interconnected;

FIG. 3 is a schematic cross-sectional diagram showing initial steps of amethod of pipe joining of the first embodiment of the present invention,employing the bridging member of FIG. 2;

FIG. 4 shows intermediate steps involved in joining the two pipestogether using the apparatus described with reference to FIGS. 2 and 3;

FIG. 5 shows the final steps involved in joining the two pipes togetherusing the apparatus described with reference to FIG. 2 to 4; and

FIGS. 6 a and 6 b show a connecting process according to a secondembodiment, using a bridging sleeve of the same form as that shown inFIG. 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The system according to the present invention facilitates the offshoreassembly of prefabricated field joints with internal liners, in a mannercompatible with field-proven techniques of pipeline assembly for S-Layor J-Lay. Furthermore, this method and apparatus for interconnectinglined pipes is designed in such a way that it would not impact thelaying rate of S-Lay or J-Lay spread. It also does not necessitate theestablishment of a fabrication base on shore. In addition, using pipereeling often requires an increase in wall thickness of the pipe toaccommodate the anticipated strain. The technique of the presentinvention, however, allows using thinner pipe, substantially reducingprocurement costs.

The interconnection process of the present invention to be described isan adaptation of the existing welding process developed for welding pipefield joints in S lay or J lay mode. Single, double or multiple pipesections with the internal liner already fitted are pre-fabricatedonshore, or on-deck. The sections may be pre-installed with componentsused during the assembly process, or the components may be providedseparately. The sections and other required components are then shippedout to the offshore site, where they are assembled to form a continuouspipeline.

FIG. 1 shows, for the sake of example only, a known pipe laying vesselupon which the novel process may be employed. This vessel corresponds tothat described in U.S. Pat. No. 5,975,802 (Willis), mentioned above. Theinvention may equally be applied in a J-Lay type vessel such as thatdescribed in U.S. Pat. No. 6,213,686 (Baugh). The vessel 5 has a deck10, on which is mounted a pipe line assembly arrangement 20, comprisingthe lined pipe interconnection system, and various coating and testingstations, for assembling a continuous pipeline from a stock of pipesegments. Pipe 30 formed in this way progresses in the direction of thearrow, over first and second radius controllers 40, 50. A tiltable ramp60 is provided for launching the pipe over the stern of vessel 5. Insolid lines, ramp 60 and other equipment are shown in a near-horizontalorientation, appropriate to lower water depths. In chain-dotted lines,the same components are shown in a steeply elevated orientation. Theradius controllers 40 to 50 guide the pipe and restrict bending withinset limits, according to the angle of the ramp 60. On ramp 60 there aremounted various pipe handling devices, such as straightener 70,tensioning and paying-out device 80 and fixed clamp 90. Sections of pipefor joining are stored in the hold of the vessel. Continuous lined pipeis formed by joining sections of pipe using the apparatus and method ofinterconnection.

The vessel is provided with swaging apparatus (not shown in FIG. 1) forinterconnecting lined pipes on the vessel, by the methods that will nowbe described in detail, with reference to the accompanying diagrams. Theswaging tool will be based at the forward end of the assemblyarrangement 20, from where it can be threaded into the open end of thepipe, and down to the location of a joint between sections. In avertical tower (J-Lay) arrangement, such as that of U.S. Pat. No.6,213,686, the swaging tool can be housed in an “attic” area at the topof the tower, to be lowered into the open end of an erect pipe section.

FIG. 2 is a cut-away diagram of a tubular bridging sleeve 102, used tobridge internally between two sections of lined pipe beinginterconnected. It comprises a hollow cylindrical tube with a smoothinterior surface of substantially equal bore, and a modified exteriorsurface, modified to enhance the seal between the sleeve and a liner,when fitted. Such modifications comprise a number of circumferentialchannels 104, grouped at each end. The recesses are used to maximise theefficiency of the seal and to enhance the grip between liner and sleeve.The sleeve therefore has three definable regions, these being a) at afirst end, a first sealing portion 106 having multiple circumferentialchannels, b) at the other end, a second sealing portion 108 havingmultiple circumferential channels and c) an elongate intermediateportion 109, interconnecting the two sealing portions. The sealingportions and their channels are described in detail, later in thedocument.

As part of the sleeve will be exposed to the fluid being transported, itneeds to be fabricated from a corrosion-resistant material. A typicalchoice of material might be Inconel™ or stainless steel, however theskilled reader will appreciate that the choice of material is notlimited to metals, but to any material providing the required physicalattributes.

Connecting Process—First Embodiment

FIG. 3 is a schematic cross-sectional diagram of two prepared lined pipesections 110, 120 being brought together for assembly with the bridgingsleeve 102. Preparation involves operations that can effectively beperformed on-shore, such as lining, end-bevelling and finishing sectionsof pipe.

The pipes 110, 120 are typically 6″ (˜150 mm) or greater in diameter,having a grade range of ×52 to ×65 and a wall thickness of at least ½(˜12 mm). The liner material is a plastic material, such as polyethyleneor polyvinylidene fluoride, of HDPE/PE100 quality, of a thickness of atleast 8 mm. The liner 130 exhibits a thermal expansion of approximately0.18 mm/m/° C. and maximum operational temperature of approximately 80°C. Service conditions for the lined pipe are a maximum external pressureof approximately 200 bars and maximum internal pressure of approximately345 bars. A typical fluid conveyed by the pipe would be deoxygenatedseawater O²<5 ppb plus biocides batch injections.

A section 110 of pipe is mid-way through the process of being connectedto a continuous pipeline 120, formed out of previously assembledsections of the same. As can be seen, the outer, steel pipe 122 is ofcontinuous diameter, although the skilled person will appreciate thatthis is not critical to the operation or efficacy of the presentinvention, applying equally to pipe including a widened end region,where the bore of the pipe is enlarged (not shown). Both ends of thepipe section are shaped in the same way, unless items other than pipesections are being fitted, such as pipe ends or flanges. The pipesection 110, 120 has been pre-lined with a plastic liner 130. The liningis dimensioned when fitted to contact the inner surfaces of the pipe,with the exception of an unlined region 144, approximately 120 mm fromthe ends to be welded, which distances the liner from the region wherehigh weld temperatures would permanently and detrimentally modify thecharacteristics of the liner. As a result, with a sleeve in place anannular void region 146 behind the weld is formed by the combination ofgaps either side of the weld. This void region ensures that there is nomaterial behind the weld region whilst the hot phase of the welding isbeing performed, thus providing the aforementioned advantages. Theunlined distance 144 can be reduced where a quicker welding time isused, as less heat is put into the weld region. The converse applies.

The two sections of pipe 110, 120 are interconnected by insertion of thesingle additional bridging sleeve 102, bridging between the internalsurfaces of the liners of both pipe sections. Prior to fitting, theprofiles of the inside and outside diameters of the sleeve aresubstantially constant and cylindrical. The ends 162, 164 of thebridging sleeve 102 and liner 130 are bevelled to ease insertion of thebridging sleeve into the bore of the liner, although the skilled personwill appreciate that only one of either needs to be bevelled, to achievesubstantially the same effect. The sleeve and liners are dimensionedsuch that the sealing portions 106, 108 are adjacent the internalsurfaces of both liners, when fitted.

In order to keep the fluid being transported from contacting any of thesusceptible steel pipe there is required a fluid-tight seal between thecontacting surfaces of the plastic liner 130 and the sleeve 102. This isachieved by swaging the sealing portions 106, 108 of the sleeve onto theliner, adjacent to a region 166 where both liner and sleeve areco-located, and which upon expansion of the sleeve by deformation forcesthe surfaces of the sleeve and plastic pipe together, thus forming afluid-tight seal and ensuring that the liner is locked in its intendedlocation. Upon application of pressure the grooves gradually bite intothe liner, providing a gradual increase in resistance as force isapplied. The grooves allow expansion to proceed in a gradual, controlledmanner using force feedback and closed-loop control. Doing so is moreeffective at providing a good seal between liner and sleeve. The lineris unable to move with respect to the steel pipe because it is grippedat both ends. When the liner is compressed by the swaging process theplastic deforms some way into circumferential channels 104. Doing sohinders any longitudinal movement of the pipe liner with respect to thesleeve, firmly capturing the liner in its intended location.

The detailed form of the grooves may be the same, for example, as thatdescribed in GB 2298256, mentioned in the introduction. The skilledperson will appreciate that different methods may be equally effectivefor adhering the contacting surfaces to each other, such as adhesives.

It is possible to have a lined section of pipe pre-fitted with a sleeveof the first embodiment. In this instance each section of pipe isprovided pre-fitted with the liner 130 and bonded sleeve 102, therebyminimising the number of operations per section performed offshore. Inprinciple, two bridging members could be fitted into both ends of eachpipe in half of the pipe sections, while the remainder of the pipesections are left with two open ends. It will generally be preferable totreat each section identically, however, rather than treat differentsets of sections differently. This preferred approach is adopted for thefollowing illustration.

All of the components necessary for joining two pipe sections togetherhave now been described. Pipe interconnection is consequently achievedin accordance with the following procedure and with reference to FIGS. 3to 5, on the basis that the first sections of pipe have already beenlaid, forming a continuous section 120 extending into the sea from thepipe laying vessel, and using the pipe sections pre-fitted with sleevesas described in the previous paragraph:

-   -   1) Lower continuous section 120 of pipe (further) into the sea        to allow the next pipe section 110 to be fitted;    -   2) Clean the mating surfaces of the protruding sleeve using, for        example, compressed air;    -   3) Lower a swaging tool 170 into the sleeve until adjacent the        lowermost sealing portion 106 of the sleeve, corresponding to        lower overlap region 166 between liner and sleeve, then radially        expand the sleeve onto the liner. (FIG. 3, Step 1);    -   4) Lower the next pipe section 110 onto the protruding sleeve        until the two ends of the steel pipes abut;    -   5) Perform a preliminary weld 180 (“root pass” and “hot”) of the        two pipes together (FIG. 4, Step 2);    -   6) During performing of the cooler phase of the welding (“weld        fill” and “cap”), swage the intermediate portion 109 of the        sleeve, in a manner that forces any fluid trapped in the region        behind the weld past the as yet unswaged region(s) (FIG. 4, Step        3);    -   7) Swage the uppermost sealing portion 108 of the sleeve (FIG.        5, Step 4), or if not performed earlier, swage both overlap        regions of the sleeve, to form in each case a seal between        sleeve and liner;    -   8) Perform any validation steps, such as non-destructive        testing;    -   9) To continue laying further pipe, repeat the process from step        1.

Note that the weld surfaces are maintained in alignment with respect toeach other during this process by the field proven interconnectionequipment, rather than by using internal clamps. Furthermore, thewelding process used is typical for S-lay and J-lay pipe laying methodscurrently in use, allowing plastic lined pipes to be used commerciallyfor subsea pipe laying. In J-Lay Systems, where the pipe is suspendedalmost vertically during the jointing process, the pre-fitting of thebridging sleeve 102 ensures that the sleeve will not slide down the boreof the pipeline. The skilled reader will appreciate that the alternativemeans can be employed, if pre-fitting is not convenient. For example, aremovable plastic collar could be provided around the intermediateportion of each bridging member, holding it in the mouth of thesuspended pipe, until it has been sealed to the liner.

Connecting Process—Second Embodiment

FIGS. 6 a and 6 b show an alternative joining process, suitable for usewith the interconnection method and apparatus.

Instead of a swaging tool being lowered into the sleeve 102 after it hasbeen installed in the pipeline, as described previously, here the sleeveand swaging tool are lowered into the pipeline as a single entity. Also,instead of a single swaging tool being radially expanded and movedlongitudinally between lower and upper sealing portions 106, 108 andintermediate portion 109 portions, there are two separate swaging tools200, 210 physically interconnected (not shown), each positioned adjacentthe upper and lower sealing portions. These can be activated with arestricted pressure to grip the sleeve, without expanding it. To effectswaging, all that is required is radial expansion of the swaging tools,eliminating the requirement for drawing the swaging tool along eachsleeve sealing portion. A further difference to the previous process isthat while the swaging tools are expanded, a seal is formed betweenthem. This is used to facilitate expansion of the intermediate 109portion, by injecting fluid such as water via pipe 220 through a port230 in the upper swaging tool 200 into the region between the tools,thus generating an expansion pressure. The gripping is also used as ameans of transporting the bridging member to the location of the joint.(Fluid or other power supply to the swaging tools 200, 210 is not shownin this schematic representation)

FIG. 6 b shows the liner after fluid expansion of the intermediateportion has been performed and the upper and lower swaging tools haveexpanded their corresponding regions. Once all swaging has beenperformed the internal fluid pressure is reduced and the swaging toolsare retracted and withdrawn from the pipe, leaving behind a sleevesimilarly shaped to that in FIG. 5, swaged by the alternative process.

Pipe interconnection in the embodiment of FIGS. 6 a and 6 b isconsequently achieved in accordance with the following procedure, on thebasis that the first sections of pipe have already been joined, forminga continuous section 120 extending into the sea from the pipe layingvessel:

-   -   1) Lower continuous section 120 of pipe (further) into the sea        to allow the next pipe section 110 to be fitted;    -   2) Clean the mating surfaces of the liners and pipes using, for        example, compressed air;    -   3) Position the next pipe section 110 such that the two ends of        the steel pipes align and abut;    -   4) Using restricted pressure in the swaging tooling 200 to 240,        grip and lower the sleeve 102 and tooling into the lined pipe        section 110 until the upper and lower sealing portions locate        adjacent the ends of the liners (as shown in FIG. 6 a);    -   5) Perform a preliminary weld 180 (“root pass” and “hot”) of the        two pipes together (FIG. 6 a, Step A);    -   6) During performing of the cooler phase 182 of the welding        (“weld fill” and “cap”) (or subsequently, if the timing for this        stage is not critical), swage by fluid injection the        intermediate portion 109 of the sleeve, in a manner that forces        any fluid trapped in the region behind the weld past the as yet        unswaged sealing portions (FIG. 6 b, Step B);    -   7) Using full pressure in the swaging tools 200, 210, swage the        lower and upper sealing portions 106, 108 of the sleeve to form        in each case a seal between sleeve and liner (FIG. 6 b, Steps C        and D);    -   8) Retract swaging tools and remove tooling;    -   9) Perform any validation steps, such as non-destructive        testing;    -   10) To continue laying further pipe, repeat the process from        step 1.

As in the first embodiment, the weld surfaces are maintained inalignment with respect to each other during this process by the fieldproven interconnection equipment, rather than by using internal clamps.Furthermore, the welding process used is typical for S-lay and J-laypipe laying methods currently in use, allowing plastic lined pipes to beused commercially for subsea pipe laying. In J-Lay Systems, where thepipe is suspended almost vertically during the jointing process, theswaging tool (which also carries the bridging member in the pipe) can besuspended from the top of a pipe lay tower or ramp, and advanced andretracted by unreeling and winching in the tether 240. The fluidpressure for expanding the intermediate portion 209 can be containedwithin an expanding bladder, rather than contained entirely by the sealsformed between the swaging tools 200, 210 and the inside of the bridgingsleeve.

In a variation of the second embodiment, the welding can begin evenbefore the bridging sleeve is located behind the joint. This may bedesirable for reasons of speed, for example, but otherwise brings noparticular advantage. It must be ensured in this case that the plasticliner does not deform in the heat of welding, so as to prevent insertionof the bridging member.

In both embodiments, the skilled person will appreciate that theindividual steps of swaging can be deferred until the most appropriatestage in the process, and as such are not rigidly bound to the orderprovided above. In all embodiments, however, the form of the bridgingsleeve, and the sequence of operation, combine to ensure that there isspace, not bridging sleeve material, at the back of the weld during theinitial passes. In general, it will be seen that the bridging sleeveproposed herein allows a much greater degree of choice in the sequenceof assembly, compared with the sleeves proposed in U.S. Pat. No.6,226,855.

Finally, note that the internal diameter of the join between pipes isnot significantly reduced by the method, allowing pigs, for example, totravel the pipeline relatively unhindered. The internal diameter of atleast the conduit may be increased at its end, so as to substantiallymaintain the bore of the liner at the joints, after expansion of thebridging member.

The skilled reader will appreciate that numerous variations are possiblewithin the principles of the apparatus described above. Accordingly itwill be understood that the embodiments illustrated herein are presentedas examples to aid understanding, and are not intended to be limiting onthe spirit or scope of the invention claimed.

1. A method of joining plastic-lined conduits comprising the followingsteps, not necessarily in the following order: providing a first conduitand a second conduit, each conduit comprising a wall of metal defining abore having an open end for connection and being substantially lined bya plastic liner, the liner ending within the bore to leave a shortunlined section at the open end of the conduit; arranging said first andsecond conduits with their ends abutting; welding said ends together toform a longer conduit; providing a tubular bridging member ofcorrosion-resistant material dimensioned to fit inside the linedconduits, the bridging member having a first sealing portion toward oneend thereof and a second sealing portion toward the second end, saidsealing portions being interconnected by an intermediate portion, thelength of said intermediate portion being sufficient to bridge theunlined portions of the abutting first and second conduits while thefirst and second sealing portions overlap said liners within the firstand second conduits respectively; with the first sealing portion of thebridging member located within the first conduit and overlapping theliner, expanding said first sealing portion radially so as to press thefirst sealing portion against the liner to form a first seal between theliner and the bridging member; and with the second sealing portion ofthe bridging member located within the second conduit and overlappingthe liner of the second conduit, expanding said second sealing portionradially so as to press the second sealing portion against the liner toform a second seal between the liner and the bridging member, wherebythe liners, the first and second seals and the bridging member form acontinuous barrier between the interior bore of the lined conduits andthe metal of the conduit walls, wherein the dimensions of the bridgingmember and the sequence of the method steps are such as to insure thatthere is space between the material of the bridging member and theinside of the abutting ends of the conduits during at least an initialpass of said welding step.
 2. A method of joining plastic-lined conduitsas claimed in claim 1, wherein the ends of the lined conduits arebrought together before the bridging member is introduced to the saidconduits at the location of the abutting ends.
 3. A method of joiningplastic-lined conduits as claimed in claim 1, wherein, after at least aninitial pass of welding has been performed between said conduits, thebridging member is installed via the said second conduit andsubsequently expanded to form a seal between the lining of each saidconduit and the bridging member.
 4. A method of joining plastic-linedconduits as claimed in claim 1, wherein the bridging member is locatedadjacent the abutting ends of the conduits prior to starting saidwelding step, the outer diameter of the bridging member being sufficientto leave a substantial gap between said conduit bore at said shortunlined section and said bridging member.
 5. A method of joiningplastic-lined conduits as claimed in claim 1, wherein at a time beforethe ends of the first and second conduits are brought together thebridging member is fitted to the first lined conduit and the firstsealing portion is expanded to form said first seal, with said secondsealing portion and part of the intermediate portion remaining outsidethe first conduit.
 6. A method of joining plastic-lined conduits asclaimed in claim 1, wherein at a time after said first pass of weldingand after introducing the bridging member at the location of theabutting ends, said intermediate portion of the bridging member isexpanded radially so as to substantially eliminate any gap between thebridging member and the inside of the abutting ends of the conduits. 7.A method of joining plastic-lined conduits as claimed in claim 6,wherein the expanding of said intermediate portion is performed prior toexpanding the first and second sealing portions, to allow escape of anyfluid trapped in said gap.
 8. A method of joining plastic-lined conduitsas claimed in claims 6, wherein the expanding of any of saidintermediate portion and first and second sealing portions is performedconcurrently with subsequent passes of welding.
 9. A method of offshorepipeline fabrication and laying, comprising the joining of first andsecond conduits by the repetition of the sequence of steps as claimed inclaim 1 to produce a continuous pipeline, each conduit being a sectionof pipeline added in turn to the pipeline being laid.
 10. A method ofoffshore pipeline fabrication and laying as claimed in claim 9, whereinsaid first conduit is the pipe section joined already to the pipelineand the second conduit becomes the first conduit after the secondconduit has been interconnected with the first conduit.
 11. A method ofoffshore pipeline fabrication and laying as claimed in claim 9, whereinsaid first conduit is the one being added to said pipeline and thesecond conduit becomes the first conduit after interconnection.
 12. Amethod of offshore pipeline fabrication and laying as claimed in claim9, wherein each said section is less than 100 m long.
 13. A method ofoffshore pipeline fabrication and laying as claimed in claim 9, whereinthe joining of the conduits is performed while the first and secondconduits are substantially horizontal, the assembled pipeline being bentfirst upwardly and then downwardly for entry into the sea.
 14. A methodof offshore pipeline fabrication and laying as claimed in claim 9wherein the joining of the conduits is performed while the first andsecond conduits are inclined at an angle for entry into the sea.
 15. Amethod of offshore pipeline fabrication and laying as claimed in claim14, wherein the method is performed upon a J-Lay vessel and theexpanding of the sealing portions of the bridging member is carried outby a swaging device mounted in the head of said tower.
 16. A method ofoffshore pipeline fabrication and laying as claimed in claim 13, whereinthe bridging member is introduced at the location of the abutting endsafter the first and second conduits have been brought together.
 17. Atubular bridging member specifically adapted for use in the methods asclaimed in claim
 1. 18. A tubular bridging member as claimed in claim 17having an outer diameter sufficient to allow free passage of thebridging member longitudinally through the lined portions of theconduits.
 19. A tubular bridging member as claimed in claim 17, whereinat least one formation is provided on each sealing portion to improvethe grip between the bridging member and the liner of the conduits. 20.A tubular bridging member as claimed in claim 19, wherein said formationcomprises a series of circumferential formations to improve the gripbetween the bridging member and the liner of the conduits.
 21. A tubularbridging member as claimed in claim 17, wherein the end of the bridgingmember is chamfered to aid insertion of said bridging member into thelined conduit.
 22. An expansion tool specifically adapted for use in themethods as claimed in claim 1, said tool performing the expansion ofportions of said tubular bridging member as claimed in claims
 17. 23. Anexpansion tool as claimed in claim 22, further comprising a means forconveying the tool to its desired location, in use.
 24. An expansiontool as claimed in claim 22, comprising a single expanding meansmoveable longitudinally to expand different portions of the bridgingmember sequentially.
 25. An expansion tool as claimed in claim 22,comprising multiple independent means for expansion of said first andsaid second sealing portions.
 26. An expansion tool as claimed in claim25, wherein said expansion means are located to permit sealing of bothportions of the tubular bridging member without disengaging said toolfrom said bridging member.
 27. An expansion tool as claimed in claim 25further comprising means for radial expansion of said intermediateportion of the tubular bridging member so as to substantially eliminatethe space between the abutting conduits and the bridging member.
 28. Anexpansion tool as claimed in claim 27, wherein said expansion of saidintermediate portion and first and second sealing portions is performedconcurrently with subsequent passes of welding.
 29. An expansion tool asclaimed in claim 27, wherein said expansion of said intermediate portionis performed by fluid injection into the region between said first andsecond radial expansion means.
 30. An expansion tool as claimed in claim29, wherein said first and second expanding means are operated with arestricted force to serve as sealing means during said fluid injection.31. A method as claimed in claim 1, wherein the bridging member is asclaimed in claim 17 and is located adjacent said abutting ends by meansof an expansion tool as claimed in claim 22, said tool engaging theinside of said bridging member by a restricted force, and then at a timeafter said member is located, using A greater force to expand saidsealing portions.
 32. A pipe laying apparatus specifically adapted forjoining lined pipes using the methods as claimed in claim
 1. 33. A pipelaying apparatus specifically adapted for joining lined pipes by amethod as claimed in claim 32 including an expansion tool as claimed inclaim
 22. 34. A plurality of lined metal pipe sections and acorresponding plurality of bridging members suitable for use inassembling a pipeline using the method as claimed in claim
 1. 35-37.(canceled)